Device and method for producing medical isotopes

ABSTRACT

A hybrid nuclear reactor for producing a medical isotope includes an ion source for producing an ion beam from a gas, a target chamber including a target that interacts with the ion beam to produce neutrons, and an activation cell positioned proximate the target chamber and including a parent material that interacts with the neutrons to produce the medical isotope via a fission reaction.

RELATED APPLICATION DATA

This application is the U.S. national stage filing of InternationalApplication No. PCT/US2009/042587 filed May 1, 2009, which claims isincorporated herein by reference in its entirety and priority to U.S.Provisional Application No. 61/050,096 filed May 2, 2008, which is fullyincorporated herein by reference in its entirety.

BACKGROUND

The invention relates to device and method for producing medicalisotopes. More particularly, the invention relates to a device andmethod for producing neutron generated medical isotopes with or withouta sub-critical reactor and low enriched uranium (LEU).

Radioisotopes are commonly used by doctors in nuclear medicine. The mostcommonly used of these isotopes is ⁹⁹Mo. Much of the supply of ⁹⁹Mo isdeveloped from highly enriched uranium (HEU). The HEU employed issufficiently enriched to make nuclear weapons. HEU is exported from theUnited States to facilitate the production of the needed ⁹⁹Mo. It isdesirable to produce the needed ⁹⁹Mo without the use of HEU.

SUMMARY

In one embodiment, the invention provides a hybrid reactor that isoperable to produce a medical isotope. The reactor includes an ionsource operable to produce an ion beam from a gas, a target chamberincluding a target that interacts with the ion beam to produce neutrons,and an activation cell positioned proximate the target chamber andincluding a parent material that interacts with the neutrons to producethe medical isotope via a fission reaction. An attenuator is positionedproximate the activation cell and selected to maintain the fissionreaction at a subcritical level, a reflector is positioned proximate thetarget chamber and selected to reflect neutrons toward the activationcell, and a moderator substantially surrounds the activation cell, theattenuator, and the reflector.

In another embodiment, the invention provides a hybrid reactor that isoperable to produce a medical isotope. The reactor includes a fusionportion including a long target path that substantially encircles aspace. The fusion portion is operable to produce a neutron flux withinthe target path. A reflector substantially surrounds the long targetpath and is arranged to reflect a portion of the neutron flux toward thespace. An activation cell is positioned within the space and includes aparent material that reacts with a portion of the neutron flux toproduce the medical isotope during a fission reaction. An attenuator ispositioned within the activation cell and is selected to maintain thefission reaction at a subcritical level and a moderator substantiallysurrounds the activation cell, the attenuator, and the reflector.

In another embodiment, the invention provides a method of producing amedical isotope. The method includes exciting a gas to produce an ionbeam, accelerating the ion beam, and passing the accelerated ion beamthrough a long target path including a target gas. The target gas andthe ions react through a fusion reaction to produce neutrons. The methodalso includes reflecting a portion of the neutrons with a reflector thatsubstantially surrounds the long target path, positioning a parentmaterial within an activation chamber adjacent the long target path, andmaintaining a fission reaction between a portion of the neutrons and theparent material to produce the medical isotope. The method furtherincludes positioning an attenuator adjacent the activation chamber andconverting a portion of the neutrons to thermal neutrons within theattenuator to enhance the fission reaction within the activationchamber.

In still another embodiment, the invention provides a method ofproducing a medical isotope. The method includes exciting a gas toproduce an ion beam, accelerating the ion beam, and passing theaccelerated ion beam through a substantially linear target pathincluding a target gas. The target gas and the ions react through afusion reaction to produce free neutrons. The method also includesreflecting a portion of the free neutrons with a reflector positionedradially outward of the target path, positioning a parent materialwithin an activation chamber adjacent the target path, and reacting thefree neutrons and the parent material to produce the medical isotopewithout the use of fissile material.

Other aspects and embodiments of the invention will become apparent byconsideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be better understood and appreciated by reference tothe detailed description of specific embodiments presented herein inconjunction with the accompanying drawings of which:

FIG. 1 is a first view of the generator with magnetic target chamber.

FIG. 2 is a second view of the generator with magnetic target chamber.

FIG. 3 is a first view of the generator with linear target chamber.

FIG. 4 is a first view of the ion source.

FIG. 5 is a sectional view of the ion source.

FIG. 6 is a first view of the accelerator.

FIG. 7 is a sectional view of the accelerator.

FIG. 8 is a first view of the differential pumping.

FIG. 9 is a sectional view of the differential pumping.

FIG. 10 is a first view of the gas filtration system.

FIG. 11 is a first view of the magnetic target chamber.

FIG. 12 is a sectional view of the magnetic target chamber.

FIG. 13 is a first view of the linear target chamber.

FIG. 14 is a sectional view of the linear target chamber, showing anexemplary isotope generation system for ¹⁸F and ¹³N production.

FIG. 15 is a first view of the generator with linear target chamber andsynchronized high speed pump.

FIG. 16 is a sectional view of the synchronized high speed pump inextraction state, allowing passage of an ion beam.

FIG. 17 is a sectional view of the synchronized high speed pump insuppression state, not allowing passage of an ion beam.

FIG. 18 is a schematic diagram of the generator with linear targetchamber and synchronized high speed pump and one embodiment ofcontroller.

FIG. 19 is a graph of stopping power (keV/μm) versus ion energy (keV)for the stopping power of ³He gas on ²H ions at 10 torr gas pressure and25° C.

FIG. 20 is a graph of stopping power (keV/μm) versus ion energy (keV)for the stopping power of ³He gas on ²H ions at 10 torr gas pressure and25° C.

FIG. 21 is a graph of fusion reaction rate (reactions/second) versus ionbeam incident energy (keV) for a 100 mA incident ²H beam impacting a ³Hetarget at 10 torr.

FIG. 22 is a perspective view of a hybrid reactor including a fusionportion and a fission portion suited to the production of medicalisotopes;

FIG. 23 is a perspective view of another arrangement of a hybrid reactorincluding a fusion portion and a fission portion suited to theproduction of medical isotopes;

FIG. 24 is a side schematic view of the fission reactor illustrating thevarious layers of material;

FIG. 25 is a top schematic view of the fission reactor of FIG. 24illustrating the various layers of material;

FIG. 26 is a side schematic view of another fission reactor illustratingthe various layers of material;

FIG. 27 is a top schematic view of the fission reactor of FIG. 26illustrating the various layers of material;

FIG. 28 is a side schematic view of another fission reactor illustratingthe various layers of material and particularly suited to the formationof ⁹⁹Mo from ⁹⁸Mo; and

FIG. 29 is a top schematic view of the fission reactor of FIG. 28illustrating the various layers of material.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass direct and indirect mountings,connections, supports, and couplings. Further, “connected” and “coupled”are not restricted to physical or mechanical connections or couplings.

Before explaining at least one embodiment, it is to be understood thatthe invention is not limited in its application to the details set forthin the following description as exemplified by the Examples. Suchdescription and Examples are not intended to limit the scope of theinvention as set forth in the appended claims. The invention is capableof other embodiments or of being practiced or carried out in variousways.

Throughout this disclosure, various aspects of this invention may bepresented in a range format. It should be understood that thedescription in range format is merely for convenience and brevity, andshould not be construed as an inflexible limitation on the scope of theinvention. Accordingly, as will be understood by one skilled in the art,for any and all purposes, particularly in terms of providing a writtendescription, all ranges disclosed herein also encompass any and allpossible subranges and combinations of subranges thereof, as well as allintegral and fractional numerical values within that range. As only oneexample, a range of 20% to 40% can be broken down into ranges of 20% to32.5% and 32.5% to 40%, 20% to 27.5% and 27.5% to 40%, etc. Any listedrange can be easily recognized as sufficiently describing and enablingthe same range being broken down into at least equal halves, thirds,quarters, fifths, tenths, etc. As a non-limiting example, each rangediscussed herein can be readily broken down into a lower third, middlethird, and upper third, etc. Further, as will also be understood by oneskilled in the art, all language such as “up to,” “at least,” “greaterthan,” “less than,” “more than” and the like include the number recitedand refer to ranges which can be subsequently broken down into subrangesas discussed above. In the same manner, all ratios disclosed herein alsoinclude all subratios falling within the broader ratio. These are onlyexamples of what is specifically intended. Further, the phrases“ranging/ranges between” a first indicate number and a second indicatenumber and “ranging/ranges from” a first indicate number “to” a secondindicate number are used herein interchangeably.

Terms such as “substantially,” “about,” “approximately” and the like areused herein to describe features and characteristics that can deviatefrom an ideal or described condition without having a significant impacton the performance of the device. For example, “substantially parallel”could be used to describe features that are desirably parallel but thatcould deviate by an angle of up to 20 degrees so long as the deviationdoes not have a significant adverse effect on the device. Similarly,“substantially linear” could include a slightly curved path or a paththat winds slightly so long as the deviation from linearity does notsignificantly adversely effect the performance of the device.

FIG. 22 illustrates an arrangement of a hybrid reactor 5 a that is wellsuited to the production of medical isotopes. Before proceeding, theterm “hybrid reactor” as used herein is meant to describe a reactor thatincludes a fusion portion and a fission portion. In particular, theillustrated reactor 5 a is well suited to the production of ⁹⁹Mo from⁹⁸Mo or from a solution of LEU. The hybrid reactor 5 a includes a fusionportion 10 and a fission portion 8 that cooperate to produce the desiredisotopes. In the construction illustrated in FIG. 22, ten distinctfusion portions 10 are employed. Each fusion portion 10 is arranged as amagnetic fusion portion 10 and acts as a neutron source as will bediscussed with regard to FIGS. 1 and 2. Of course other arrangementscould use fewer fusion portions 10, more fusion portions 10, or otherarrangements of fusion portions as desired.

FIG. 23 illustrates another arrangement of a hybrid reactor 5 b that iswell suited to the production of medical isotopes. In the constructionof FIG. 23, linear fusion portions 11 act as neutron sources as will bediscussed with regard to FIGS. 3 and 4. In the construction of FIG. 23,the linear fusion portions 11 are arranged such that five fusionportions 11 are positioned at one end of the fission portion 8 and fivefusion portions 11 are positioned on the opposite end of the fissionportion 8. Of course other arrangements that employ other quantities offusion portions 11, or other arrangements of fusion portions could beemployed if desired.

As illustrated in FIGS. 1-3, each fusion portion 10, 11 provides acompact device that may function as a high energy proton source or aneutron source. In one embodiment, the fusion portions 10, 11 utilize²H—³He (deuterium-helium 3) fusion reactions to generate protons, whichmay then be used to generate other isotopes. In another embodiment, thefusion portions 10, 11 function as neutron sources by changing the basereactions to ²H—³H, ²H—²H, or ³H—³H reactions.

In view of the disadvantages inherent in the conventional types ofproton or neutron sources, the fusion portions 10, 11 provide a novelhigh energy proton or neutron source (sometimes referred to hereingenerically as an ion source but also considered a particle source) thatmay be utilized for the production of medical isotopes. Each fusionportion 10, 11 uses a small amount of energy to create a fusionreaction, which then creates higher energy protons or neutrons that maybe used for isotope production. Using a small amount of energy may allowthe device to be more compact than previous conventional devices.

Each fusion portion 10, 11 suitably generates protons that may be usedto generate other isotopes including but not limited to ¹⁸F, ¹¹C, ¹⁵O,¹³N, ⁶³Zn, ¹²⁴I and many others. By changing fuel types, each fusionportion may also be used to generate high fluxes of neutrons that may beused to generate isotopes including but not limited to ¹³¹I, ¹³³Xe,¹¹¹In, ¹²⁵I, ⁹⁹Mo (which decays to ^(99m)Tc) and many others. As such,each fusion portion 10, 11 provides a novel compact high energy protonor neutron source for uses such as medical isotope generation that hasmany of the advantages over the proton or neutron sources mentionedheretofore.

In general, each fusion portion 10, 11 provides an apparatus forgenerating protons or neutrons, which, in turn, are suitably used togenerate a variety of radionuclides (or radioisotopes). With referenceto FIGS. 1 and 2, each magnetic fusion portion 10 includes a plasma ionsource 20, which may suitably include an RF-driven ion generator and/orantenna 24, an accelerator 30, which is suitably electrode-driven, and atarget system including a target chamber 60. In the case of proton-basedradioisotope production, the apparatus may also include an isotopeextraction system 90. The RF-driven plasma ion source 20 generates andcollimates an ion beam directed along a predetermined pathway, whereinthe ion source 20 includes an inlet for entry of a first fluid. Theelectrode-driven accelerator 30 receives the ion beam and acceleratesthe ion beam to yield an accelerated ion beam. The target systemreceives the accelerated ion beam. The target system contains a nuclearparticle-deriving, e.g. a proton-deriving or neutron-deriving, targetmaterial that is reactive with the accelerated beam and that, in turn,emits nuclear particles, i.e., protons or neutrons. For radioisotopeproduction, the target system may have sidewalls that are transparent tothe nuclear particles. An isotope extraction system 90 is disposedproximate or inside the target system and contains an isotope-derivingmaterial that is reactive to the nuclear particles to yield aradionuclide (or radioisotope).

It should be noted that while an RF-driven ion generator or ion sourceis described herein, other systems and devices are also well-suited togenerating the desired ions. For example, other constructions couldemploy a DC arc source in place of or in conjunction with the RF-drivenion generator or ion source. Still other constructions could use hotcathode ion sources, cold cathode ion sources, laser ion sources, fieldemission sources, and/or field evaporation sources in place of or inconjunction with a DC arc source and or an RF-driven ion generator orion source. As such, the invention should not be limited toconstructions that employ an RF-driven ion generator or ion source.

As discussed, the fusion portion can be arranged in a magneticconfiguration 10 and/or a linear configuration 11. The six majorsections or components of the device are connected as shown in FIG. 1and FIG. 2 for the magnetic configuration 10, and FIG. 3 for the linearconfiguration 11. Each fusion portion, whether arranged in the magneticarrangement or the linear arrangement includes an ion source generallydesignated 20, an accelerator 30, a differential pumping system 40, atarget system which includes a target chamber 60 for the magneticconfiguration 10 or a target chamber 70 for the linear configuration 11,an ion confinement system generally designated 80, and an isotopeextraction system generally designated 90. Each fusion portion mayadditionally include a gas filtration system 50. Each fusion portion mayalso include a synchronized high speed pump 100 in place of or inaddition to the differential pumping system 40. Pump 100 is especiallyoperative with the linear configuration of the target chamber.

The ion source 20 (FIG. 4 and FIG. 5) includes a vacuum chamber 25, aradio-frequency (RF) antenna 24, and an ion injector 26 having an ioninjector first stage 23 and an ion injector final stage 35 (FIG. 6). Amagnet (not shown) may be included to allow the ion source to operate ina high density helicon mode to create higher density plasma 22 to yieldmore ion current. The field strength of this magnet suitably ranges fromabout 50 G to about 6000 G, suitably about 100 G to about 5000 G. Themagnets may be oriented so as to create an axial field (north-southorientation parallel to the path of the ion beam) or a cusp field(north-south orientation perpendicular to the path of the ion beam withthe inner pole alternating between north and south for adjacentmagnets). An axial field can create a helicon mode (dense plasma),whereas a cusp field may generate a dense plasma but not a heliconinductive mode. A gas inlet 21 is located on one end of the vacuumchamber 25, and the first stage 23 of the ion injector 26 is on theother. Gas inlet 21 provides one of the desired fuel types, which mayinclude ¹H₂, ²H₂, ³H₂, ³He, and ¹¹B, or may comprise ¹H, ²H, ³H, ³He,and ¹¹B. The gas flow at inlet 21 is suitably regulated by a mass flowcontroller (not shown), which may be user or automatically controlled.RF antenna 24 is suitably wrapped around the outside of vacuum chamber25. Alternatively, RF antenna 24 may be inside vacuum chamber 25.Suitably, RF antenna 24 is proximate the vacuum chamber such that radiofrequency radiation emitted by RF antenna 24 excites the contents (i.e.,fuel gas) of vacuum chamber 25, for example, forming a plasma. RFantenna 24 includes a tube 27 of one or more turns. RF tube or wire 27may be made of a conductive and bendable material such as copper,aluminum, or stainless steel.

Ion injector 26 includes one or more shaped stages (23, 35). Each stageof the ion injector includes an acceleration electrode 32 suitably madefrom conductive materials that may include metals and alloys to provideeffective collimation of the ion beam. For example, the electrodes aresuitably made from a conductive metal with a low sputtering coefficient,e.g., tungsten. Other suitable materials may include aluminum, steel,stainless steel, graphite, molybdenum, tantalum, and others. RF antenna24 is connected at one end to the output of an RF impedance matchingcircuit (not shown) and at the other end to ground. The RF impedancematching circuit may tune the antenna to match the impedance required bythe generator and establish an RF resonance. RF antenna 24 suitablygenerates a wide range of RF frequencies, including but not limited to 0Hz to tens of kHz to tens of MHz to GHz and greater. RF antenna 24 maybe water-cooled by an external water cooler (not shown) so that it cantolerate high power dissipation with a minimal change in resistance. Thematching circuit in a turn of RF antenna 24 may be connected to an RFpower generator (not shown). Ion source 20, the matching circuit, andthe RF power generator may be floating (isolated from ground) at thehighest accelerator potential or slightly higher, and this potential maybe obtained by an electrical connection to a high voltage power supply.RF power generator may be remotely adjustable, so that the beamintensity may be controlled by the user, or alternatively, by computersystem. RF antenna 24 connected to vacuum chamber 25 suitably positivelyionizes the fuel, creating an ion beam. Alternative means for creatingions are known by those of skill in the art and may include microwavedischarge, electron-impact ionization, and laser ionization.

Accelerator 30 (FIG. 6 and FIG. 7) suitably includes a vacuum chamber36, connected at one end to ion source 20 via an ion source matingflange 31, and connected at the other end to differential pumping system40 via a differential pumping mating flange 33. The first stage of theaccelerator is also the final stage 35 of ion injector 26. At least onecircular acceleration electrode 32, and suitably 3 to 50, more suitably3 to 20, may be spaced along the axis of accelerator vacuum chamber 36and penetrate accelerator vacuum chamber 36, while allowing for a vacuumboundary to be maintained. Acceleration electrodes 32 have holes throughtheir centers (smaller than the bore of the accelerator chamber) and aresuitably each centered on the longitudinal axis (from the ion source endto the differential pumping end) of the accelerator vacuum chamber forpassage of the ion beam. The minimum diameter of the hole inacceleration electrode 32 increases with the strength of the ion beam orwith multiple ion beams and may range from about 1 mm to about 20 cm indiameter, and suitably from about 1 mm to about 6 cm in diameter.Outside vacuum chamber 36, acceleration electrodes 32 may be connectedto anti-corona rings 34 that decrease the electric field and minimizecorona discharges. These rings may be immersed in a dielectric oil or aninsulating dielectric gas such as SF₆. Suitably, a differential pumpingmating flange 33, which facilitates connection to differential pumpingsection 40, is at the exit of the accelerator.

Each acceleration electrode 32 of accelerator 30 can be supplied biaseither from high voltage power supplies (not shown), or from a resistivedivider network (not shown) as is known by those of skill in the art.The divider for most cases may be the most suitable configuration due toits simplicity. In the configuration with a resistive divider network,the ion source end of the accelerator may be connected to the highvoltage power supply, and the second to last accelerator electrode 32may be connected to ground. The intermediate voltages of the acceleratorelectrodes 32 may be set by the resistive divider. The final stage ofthe accelerator is suitably biased negatively via the last accelerationelectrode to prevent electrons from the target chamber from streamingback into accelerator 30.

In an alternate embodiment, a linac (for example, a RF quadrapole) maybe used instead of an accelerator 30 as described above. A linac mayhave reduced efficiency and be larger in size compared to accelerator 30described above. The linac may be connected to ion source 20 at a firstend and connected to differential pumping system 40 at the other end.Linacs may use RF instead of direct current and high voltage to obtainhigh particle energies, and they may be constructed as is known in theart.

Differential pumping system 40 (FIG. 8 and FIG. 9) includes pressurereducing barriers 42 that suitably separate differential pumping system40 into at least one stage. Pressure reducing barriers 42 each suitablyinclude a thin solid plate or one or more long narrow tubes, typically 1cm to 10 cm in diameter with a small hole in the center, suitably about0.1 mm to about 10 cm in diameter, and more suitably about 1 mm to about6 cm. Each stage comprises a vacuum chamber 44, associated pressurereducing barriers 42, and vacuum pumps 17, each with a vacuum pumpexhaust 41. Each vacuum chamber 44 may have 1 or more, suitably 1 to 4,vacuum pumps 17, depending on whether it is a 3, 4, 5, or 6 port vacuumchamber 44. Two of the ports of the vacuum chamber 44 are suitablyoriented on the beamline and used for ion beam entrance and exit fromdifferential pumping system 40. The ports of each vacuum chamber 44 mayalso be in the same location as pressure reducing barriers 42. Theremaining ports of each vacuum chamber 44 are suitably connected byconflat flanges to vacuum pumps 17 or may be connected to variousinstrumentation or control devices. The exhaust from vacuum pumps 17 isfed via vacuum pump exhaust 41 into an additional vacuum pump orcompressor if necessary (not shown) and fed into gas filtration system50. Alternatively, if needed, this additional vacuum pump may be locatedin between gas filtration system 50 and target chamber 60 or 70. Ifthere is an additional compression stage, it may be between vacuum pumps17 and filtration system 50. Differential pumping section is connectedat one end to the accelerator 30 via an accelerator mating flange 45,and at the other at beam exit port 46 to target chamber (60 or 70) via atarget chamber mating flange 43. Differential pumping system 40 may alsoinclude a turbulence generating apparatus (not shown) to disrupt laminarflow. A turbulence generating apparatus may restrict the flow of fluidand may include surface bumps or other features or combinations thereofto disrupt laminar flow. Turbulent flow is typically slower than laminarflow and may therefore decrease the rate of fluid leakage from thetarget chamber into the differential pumping section.

In some constructions, the pressure reducing barriers 42 are replaced orenhanced by plasma windows. Plasma windows include a small hole similarto those employed as pressure reducing barriers. However, a dense plasmais formed over the hole to inhibit the flow of gas through the smallhole while still allowing the ion beam to pass. A magnetic or electricfield is formed in or near the hole to hold the plasma in place.

Gas filtration system 50 is suitably connected at its vacuum pumpisolation valves 51 to vacuum pump exhausts 41 of differential pumpingsystem 40 or to additional compressors (not shown). Gas filtrationsystem 50 (FIG. 10) includes one or more pressure chambers or “traps”(13, 15) over which vacuum pump exhaust 41 flows. The traps suitablycapture fluid impurities that may escape the target chamber or ionsource, which, for example, may have leaked into the system from theatmosphere. The traps may be cooled to cryogenic temperatures withliquid nitrogen (LN traps, 15). As such, cold liquid traps 13, 15suitably cause gas such as atmospheric contaminants to liquefy andremain in traps 13, 15. After flowing over one or more LN traps 15connected in series, the gas is suitably routed to a titanium gettertrap 13, which absorbs contaminant hydrogen gasses such as deuteriumthat may escape the target chamber or the ion source and may otherwisecontaminate the target chamber. The outlet of getter trap 13 is suitablyconnected to target chamber 60 or 70 via target chamber isolation valve52 of gas filtration system 50. Gas filtration system 50 may be removedaltogether from device 10, if one wants to constantly flow gas into thesystem and exhaust it out vacuum pump exhaust 41, to another vacuum pumpexhaust (not shown), and to the outside of the system. Without gasfiltration system 50, operation of apparatus 10 would not be materiallyaltered. Apparatus 10, functioning as a neutron source, may not includegetter trap 13 of gas filtration system 50.

Vacuum pump isolation valves 51 and target chamber isolation valves 52may facilitate gas filtration system 50 to be isolated from the rest ofthe device and connected to an external pump (not shown) via pump-outvalve 53 when the traps become saturated with gas. As such, if vacuumpump isolation valves 51 and target chamber isolation valves 52 areclosed, pump-out valves 53 can be opened to pump out impurities.

Target chamber 60 (FIG. 11 and FIG. 12 for magnetic system 10) or targetchamber 70 (FIG. 13 and FIG. 14 for the linear system 11) may be filledwith the target gas to a pressure of about 0 to about 100 torr, about100 mtorr to about 30 torr, suitably about 0.1 to about 10 torr,suitably about 100 mtorr to about 30 torr. The specific geometry oftarget chamber 60 or 70 may vary depending on its primary applicationand may include many variations. The target chamber may suitably be acylinder about 10 cm to about 5 m long, and about 5 mm to about 100 cmin diameter for the linear system 14. When used in the hybrid reactor,the target chamber is arranged to provide an activation column in itscenter. The fusion portions are arranged to direct beams through thetarget chamber but outside of the activation column. Thus, the beamstravel substantially within an annular space. Suitably, target chamber70 may be about 0.1 m to about 2 m long, and about 30 to 50 cm indiameter for the linear system 14.

For the magnetic system 12, target chamber 60 may resemble a thickpancake, about 10 cm to about 1 m tall and about 10 cm to about 10 m indiameter. Suitably, the target chamber 60 for the magnetic system 12 maybe about 20 cm to about 50 cm tall and approximately 50 cm in diameter.For the magnetic target chamber 60, a pair of either permanent magnetsor electromagnets (ion confinement magnet 12) may be located on thefaces of the pancake, outside of the vacuum walls or around the outerdiameter of the target chamber (see FIG. 11 and FIG. 12). The magnetsare suitably made of materials including but not limited to copper andaluminum, or superconductors or NdFeB for electromagnets. The poles ofthe magnets may be oriented such that they create an axial magneticfield in the bulk volume of the target chamber. The magnetic field issuitably controlled with a magnetic circuit comprising high permeabilitymagnetic materials such as 1010 steel, mu-metal, or other materials. Thesize of the magnetic target chamber and the magnetic beam energydetermine the field strength according to equation (1):r=1.44√{square root over (E)}/B  (1)for deuterons, wherein r is in meters, E is the beam energy in eV, and Bis the magnetic field strength in gauss. The magnets may be orientedparallel to the flat faces of the pancake and polarized so that amagnetic field exists that is perpendicular to the direction of the beamfrom the accelerator 30, that is, the magnets may be mounted to the topand bottom of the chamber to cause ion recirculation. In anotherembodiment employing magnetic target chamber 60, there are suitablyadditional magnets on the top and bottom of the target chamber to createmirror fields on either end of the magnetic target chamber (top andbottom) that create localized regions of stronger magnetic field at bothends of the target chamber, creating a mirror effect that causes the ionbeam to be reflected away from the ends of the target chamber. Theseadditional magnets creating the mirror fields may be permanent magnetsor electromagnets. It is also desirable to provide a stronger magneticfield near the radial edge of the target chamber to create a similarmirror effect. Again, a shaped magnetic circuit or additional magnetscould be employed to provide the desired strong magnetic field. One endof the target chamber is operatively connected to differential pumpingsystem 40 via differential pumping mating flange 33, and a gasrecirculation port 62 allows for gas to re-enter the target chamber fromgas filtration system 50. The target chamber may also includefeedthrough ports (not shown) to allow for various isotope generatingapparatus to be connected.

In the magnetic configuration of the target chamber 60, the magneticfield confines the ions in the target chamber. In the linearconfiguration of the target chamber 70, the injected ions are confinedby the target gas. When used as a proton or neutron source, the targetchamber may require shielding to protect the operator of the device fromradiation, and the shielding may be provided by concrete walls suitablyat least one foot thick. Alternatively, the device may be storedunderground or in a bunker, distanced away from users, or water or otherfluid may be used a shield, or combinations thereof.

Both differential pumping system 40 and gas filtration system 50 mayfeed into the target chamber 60 or 70. Differential pumping system 40suitably provides the ion beam, while gas filtration system 50 suppliesa stream of filtered gas to fill the target chamber. Additionally, inthe case of isotope generation, a vacuum feedthrough (not shown) may bemounted to target chamber 60 or 70 to allow the isotope extractionsystem 90 to be connected to the outside.

Isotope extraction system 90, including the isotope generation system63, may be any number of configurations to provide parent compounds ormaterials and remove isotopes generated inside or proximate the targetchamber. For example, isotope generation system 63 may include anactivation tube 64 (FIGS. 12 and 14) that is a tightly wound helix thatfits just inside the cylindrical target chamber and having walls 65.Alternatively, in the case of the pancake target chamber with an ionconfinement system 80, it may include a helix that covers the devicealong the circumference of the pancake and two spirals, one each on thetop and bottom faces of the pancake, all connected in series. Walls 65of activation tubes 64 used in these configurations are sufficientlystrong to withstand rupture, yet sufficiently thin so that protons ofover 14 MeV (approximately 10 to 20 MeV) may pass through them whilestill keeping most of their energy. Depending on the material, the wallsof the tubing may be about 0.01 mm to about 1 mm thick, and suitablyabout 0.1 mm thick. The walls of the tubing are suitably made ofmaterials that will not generate neutrons. The thin-walled tubing may bemade from materials such as aluminum, carbon, copper, titanium, orstainless steel. Feedthroughs (not shown) may connect activation tube 64to the outside of the system, where the daughter or productcompound-rich fluid may go to a heat exchanger (not shown) for coolingand a chemical separator (not shown) where the daughter or productisotope compounds are separated from the mixture of parent compounds,daughter compounds, and impurities.

In another construction, shown in FIG. 15, a high speed pump 100 ispositioned in between accelerator 30 and target chamber 60 or 70. Highspeed pump 100 may replace the differential pumping system 40 and/or gasfiltration system 50. The high speed pump suitably includes one or moreblades or rotors 102 and a timing signal 104 that is operativelyconnected to a controller 108. The high speed pump may be synchronizedwith the ion beam flow from the accelerator section, such that the ionbeam or beams are allowed to pass through at least one gap 106 inbetween or in blades 102 at times when gaps 106 are aligned with the ionbeam. Timing signal 104 may be created by having one or more markersalong the pump shaft or on at least one of the blades. The markers maybe optical or magnetic or other suitable markers known in the art.Timing signal 104 may indicate the position of blades 102 or gap 106 andwhether or not there is a gap aligned with the ion beam to allow passageof the ion beam from first stage 35 of accelerator 30 through high speedpump 100 to target chamber 60 or 70. Timing signal 104 may be used as agate pulse switch on the ion beam extraction voltage to allow the ionbeam to exit ion source 20 and accelerator 30 and enter high speed pump100. When flowing through the system from ion source 20 to accelerator30 to high speed pump 100 and to target chamber 60 or 70, the beam maystay on for a time period that the ion beam and gap 106 are aligned andthen turn off before and while the ion beam and gap 106 are not aligned.The coordination of timing signal 104 and the ion beam may becoordinated by a controller 108. In one embodiment of controller 108(FIG. 18), controller 108 may comprise a pulse processing unit 110, ahigh voltage isolation unit 112, and a high speed switch 114 to controlthe voltage of accelerator 30 between suppression voltage (ion beam off;difference may be 5-10 kV) and extraction voltage (ion beam on;difference may be 20 kv). Timing signal 104 suitably creates a logicpulse that is passed through delay or other logic or suitable meansknown in the art. Pulse processing unit 110 may alter the turbine of thehigh speed pump to accommodate for delays, and high speed switch 114 maybe a MOSFET switch or other suitable switch technology known in the art.High voltage isolation unit 112 may be a fiber optic connection or othersuitable connections known in the art. For example, the timing signal104 may indicate the presence or absence of a gap 106 only once perrotation of a blade 102, and the single pulse may signal a set ofelectronics via controller 108 to generate a set of n pulses per bladerevolution, wherein n gaps are present in one blade rotation.Alternatively, timing signal 104 may indicate the presence or absence ofa gap 106 for each of m gaps during a blade rotation, and the m pulsesmay each signal a set of electronics via controller 108 to generate apulse per blade revolution, wherein m gaps are present in one bladerotation. The logic pulses may be passed or coordinated via controller108 to the first stage of accelerator section 35 (ion extractor), suchthat the logic pulse triggers the first stage of accelerator section 35to change from a suppression state to an extraction state and visaversa. If the accelerator were +300 kV, for example, the first stage ofaccelerator 35 may be biased to +295 kV when there is no gap 106 in highspeed pump 100, so that the positive ion beam will not flow from +295 kVto +300 kV, and the first stage of accelerator 35 may be biased to +310kV when there is a gap 106 in high speed pump 100, so that the ion beamtravels through accelerator 30 and through gaps 106 in high speed pump100 to target chamber 60 or 70. The difference in voltage between thesuppression and extraction states may be a relatively small change, suchas about 1 kV to about 50 kV, suitably about 10 kV to about 20 kV. Asmall change in voltage may facilitate a quick change betweensuppression (FIG. 17) and extraction (FIG. 16) states. Timing signal 104and controller 108 may operate by any suitable means known in the art,including but not limited to semiconductors and fiber optics. The periodof time that the ion beam is on and off may depend on factors such asthe rotational speed of blades 102, the number of blades or gaps 106,and the dimensions of the blades or gaps.

The isotopes ¹⁸F and ¹³N, which are utilized in PET scans, may begenerated from the nuclear reactions inside each fusion portion using anarrangement as illustrated in FIGS. 12 and 14. These isotopes can becreated from their parent isotopes, ¹⁸O (for ¹⁸F) and ¹⁶O (for ¹³N) byproton bombardment. The source of the parent may be a fluid, such aswater (H₂ ¹⁸O or H₂ ¹⁶O), that may flow through the isotope generationsystem via an external pumping system (not shown) and react with thehigh energy protons in the target chamber to create the desired daughtercompound. For the production of ¹⁸F or ¹³N, water (H₂ ¹⁸O or H₂ ¹⁶O,respectively) is flowed through isotope generation system 63, and thehigh energy protons created from the aforementioned fusion reactions maypenetrate tube 64 walls and impact the parent compound and cause (p,α)reactions producing ¹⁸F or ¹³N. In a closed system, for example, theisotope-rich water may then be circulated through the heat exchanger(not shown) to cool the fluid and then into the chemical filter (notshown), such as an ion exchange resin, to separate the isotope from thefluid. The water mixture may then recirculate into target chamber (60 or70), while the isotopes are stored in a filter, syringe, or by othersuitable means known in the art until enough has been produced forimaging or other procedures.

While a tubular spiral has been described, there are many othergeometries that could be used to produce the same or otherradionuclides. For example, isotope generation system 63 may suitably beparallel loops or flat panel with ribs. In another embodiment, a waterjacket may be attached to the vacuum chamber wall. For ¹⁸F or ¹³Ncreation, the spiral could be replaced by any number of thin walledgeometries including thin windows, or could be replaced by a solidsubstance that contained a high oxygen concentration, and would beremoved and processed after transmutation. Other isotopes can begenerated by other means.

With reference to FIGS. 1 and 3, the operation of the fusion portionswill now be described. Before operation of one of the fusion portions,the respective target chamber 60 or 70 is suitably filled by firstpre-flowing the target gas, such as ³He, through the ion source 20 withthe power off, allowing the gas to flow through the apparatus 10 andinto the target chamber. In operation, a reactant gas such as ²H₂ entersthe ion source 20 and is positively ionized by the RF field to formplasma 22. As plasma 22 inside vacuum chamber 25 expands toward ioninjector 26, plasma 22 starts to be affected by the more negativepotential in accelerator 30. This causes the positively charged ions toaccelerate toward target chamber 60 or 70. Acceleration electrodes 32 ofthe stages (23 and 35) in ion source 20 collimate the ion beam or beams,giving each a nearly uniform ion beam profile across the first stage ofaccelerator 30. Alternatively, the first stage of accelerator 30 mayenable pulsing or on/off switching of the ion beam, as described above.As the beam continues to travel through accelerator 30, it picks upadditional energy at each stage, reaching energies of up to 5 MeV, up to1 MeV, suitably up to 500 keV, suitably 50 keV to 5 MeV, suitably 50 keVto 500 keV, and suitably 0 to 10 Amps, suitably 10 to 100 mAmps, by thetime it reaches the last stage of the accelerator 30. This potential issupplied by an external power source (not shown) capable of producingthe desired voltage. Some neutral gas from ion source 20 may also leakout into accelerator 30, but the pressure in accelerator 30 will be keptto a minimum by differential pumping system 40 or synchronized highspeed pump 100 to prevent excessive pressure and system breakdown. Thebeam continues at high velocity into differential pumping 40 where itpasses through the relatively low pressure, short path length stageswith minimal interaction. From here it continues into target chamber 60or 70, impacting the high density target gas that is suitably 0 to 100torr, suitably 100 mtorr to 30 torr, suitably 5 to 20 torr, slowing downand creating nuclear reactions. The emitted nuclear particles may beabout 0.3 MeV to about 30 MeV protons, suitably about 10 MeV to about 20MeV protons, or about 0.1 MeV to about 30 MeV neutrons, suitably about 2MeV to about 20 MeV neutrons.

In the embodiment of linear target chamber 70, the ion beam continues inan approximately straight line and impacts the high density target gasto create nuclear reactions until it stops.

In the embodiment of magnetic target chamber 60, the ion beam is bentinto an approximately helical path, with the radius of the orbit (fordeuterium ions, ²H) given by the equation (2):

$\begin{matrix}{r = \frac{204*\sqrt{E_{i}}}{B}} & (2)\end{matrix}$where r is the orbital radius in cm, E_(i), is the ion energy in eV, andB is the magnetic field strength in gauss. For the case of a 500 keVdeuterium beam and a magnetic field strength of 7 kG, the orbital radiusis about 20.6 cm and suitably fits inside a 25 cm radius chamber. Whileion neutralization can occur, the rate at which re-ionization occurs ismuch faster, and the particle will spend the vast majority of its timeas an ion.

Once trapped in this magnetic field, the ions orbit until the ion beamstops, achieving a very long path length in a short chamber. Due to thisincreased path length relative to linear target chamber 70, magnetictarget chamber 60 can also operate at lower pressure. Magnetic targetchamber 60, thus, may be the more suitable configuration. A magnetictarget chamber can be smaller than a linear target chamber and stillmaintain a long path length, because the beam may recirculate many timeswithin the same space. The fusion products may be more concentrated inthe smaller chamber. As explained, a magnetic target chamber may operateat lower pressure than a linear chamber, easing the burden on thepumping system because the longer path length may give the same totalnumber of collisions with a lower pressure gas as with a short pathlength and a higher pressure gas of the linac chamber.

Due to the pressure gradient between accelerator 30 and target chamber60 or 70, gas may flow out of the target chamber and into differentialpumping system 40. Vacuum pumps 17 may remove this gas quickly,achieving a pressure reduction of approximately 10 to 100 times orgreater. This “leaked” gas is then filtered and recycled via gasfiltration system 50 and pumped back into the target chamber, providingmore efficient operation. Alternatively, high speed pump 100 may beoriented such that flow is in the direction back into the targetchamber, preventing gas from flowing out of the target chamber.

While the invention described herein is directed to a hybrid reactor, itis possible to produce certain isotopes using the fusion portion alone.If this is desired, an isotope extraction system 90 as described hereinis inserted into target chamber 60 or 70. This device allows the highenergy protons to interact with the parent nuclide of the desiredisotope. For the case of ¹⁸F production or ¹³N production, this targetmay be water-based (¹⁶O for ¹³N, and ¹⁸O for ¹⁸F) and will flow throughthin-walled tubing. The wall thickness is thin enough that the 14.7 MeVprotons generated from the fusion reactions will pass through themwithout losing substantial energy, allowing them to transmute the parentisotope to the desired daughter isotope. The ¹³N or ¹⁸F rich water thenis filtered and cooled via external system. Other isotopes, such as ¹²⁴I(from ¹²⁴Te or others), ¹¹C (from ¹⁴N or ¹¹B or others), ¹⁵O (from ¹⁵Nor others), and ⁶³Zn, may also be generated. In constructions thatemploy the fission portion to generate the desired isotopes, the isotopeextraction system 90 can be omitted.

If the desired product is protons for some other purpose, target chamber60 or 70 may be connected to another apparatus to provide high energyprotons to these applications. For example, the a fusion portion may beused as an ion source for proton therapy, wherein a beam of protons isaccelerated and used to irradiate cancer cells.

If the desired product is neutrons, no hardware such as isotopeextraction system 90 is required, as the neutrons may penetrate thewalls of the vacuum system with little attenuation. For neutronproduction, the fuel in the injector is changed to either deuterium ortritium, with the target material changed to either tritium ordeuterium, respectively. Neutron yields of up to about 10¹⁵ neutrons/secor more may be generated. Additionally, getter trap 13 may be removed.The parent isotope compound may be mounted around target chamber 60 or70, and the released neutrons may convert the parent isotope compound tothe desired daughter isotope compound. Alternatively, an isotopeextraction system may still or additionally be used inside or proximalto the target chamber. A moderator (not shown) that slows neutrons maybe used to increase the efficiency of neutron interaction. Moderators inneutronics terms may be any material or materials that slow downneutrons. Suitable moderators may be made of materials with low atomicmass that are unlikely to absorb thermal neutrons. For example, togenerate ⁹⁹Mo from a ⁹⁸Mo parent compound, a water moderator may beused. ⁹⁹Mo decays to ^(99m)Tc, which may be used for medical imagingprocedures. Other isotopes, such as ¹³¹I, ¹³³Xe, ¹¹¹In, and ¹²⁵I, mayalso be generated. When used as a neutron source, the fusion portion mayinclude shielding such as concrete or a fluid such as water at least onefoot thick to protect the operators from radiation. Alternatively, theneutron source may be stored underground to protect the operators fromradiation. The manner of usage and operation of the invention in theneutron mode is the same as practiced in the above description.

The fusion rate of the beam impacting a thick target gas can becalculated. The incremental fusion rate for the ion beam impacting athick target gas is given by the equation (3):

$\begin{matrix}{{{df}(E)} = {n_{b}*\frac{I_{ion}}{e}*{\sigma(E)}*{\mathbb{d}l}}} & (3)\end{matrix}$where df(E) is the fusion rate (reactions/sec) in the differentialenergy interval dE, n_(b) is the target gas density (particles/m³),I_(ion) is the ion current (A), e is the fundamental charge of1.6022*10⁻¹⁹ coulombs/particle, σ(E) is the energy dependent crosssection (m²) and dl is the incremental path length at which the particleenergy is E. Since the particle is slowing down once inside the target,the particle is only at energy E over an infinitesimal path length.

To calculate the total fusion rate from a beam stopping in a gas,equation (2) is integrated over the entire particle path length fromwhere its energy is at its maximum of E_(i) to where it stops as shownin equation (4):

$\begin{matrix}{{F\left( E_{i} \right)} = {{\int_{0}^{E_{i}}{n_{b}*\frac{I_{ion}}{e}*{\sigma(E)}\ {\mathbb{d}l}}} = {\frac{n_{b}I_{ion}}{e}{\int_{0}^{E_{i}}{{\sigma(E)}\ {\mathbb{d}l}}}}}} & (4)\end{matrix}$where F(E_(i)) is the total fusion rate for a beam of initial energyE_(i) stopping in the gas target. To solve this equation, theincremental path length dl is solved for in terms of energy. Thisrelationship is determined by the stopping power of the gas, which is anexperimentally measured function, and can be fit by various types offunctions. Since these fits and fits of the fusion cross section tend tobe somewhat complicated, these integrals were solved numerically. Datafor the stopping of deuterium in ³He gas at 10 torr and 25° C. wasobtained from the computer program Stopping and Range of Ions in Matter(SRIM; James Ziegler, www.srim.org) and is shown in FIG. 19.

An equation was used to predict intermediate values. A polynomial oforder ten was fit to the data shown in FIG. 19. The coefficients areshown in TABLE 1, and resultant fit with the best-fit 10^(th) orderpolynomial is shown in FIG. 20.

TABLE 1 Order Coefficient 10 −1.416621E−27 9 3.815365E−24 8−4.444877E−21 7 2.932194E−18 6 −1.203915E−15 5 3.184518E−13 4−5.434029E−11 3 5.847578E−09 2 −3.832260E−07 1 1.498854E−05 0−8.529514E−05

As can be seen from these data, the fit was quite accurate over theenergy range being considered. This relationship allowed the incrementalpath length, dl, to be related to an incremental energy interval by thepolynomial tabulated above. To numerically solve this, it is suitable tochoose either a constant length step or a constant energy step, andcalculate either how much energy the particle has lost or how far it hasgone in that step. Since the fusion rate in equation (4) is in terms ofdl, a constant length step was the method used. The recursiverelationship for the particle energy E as it travels through the targetis the equation (5):E _(n+1) =E _(n) −S(E)*dl  (5)where n is the current step (n=0 is the initial step, and E_(o) is theinitial particle energy), E_(n+1) is the energy in the next incrementalstep, S(E) is the polynomial shown above that relates the particleenergy to the stopping power, and dl is the size of an incremental step.For the form of the incremental energy shown above, E is in keV and dlis in μm.

This formula yields a way to determine the particle energy as it movesthrough the plasma, and this is important because it facilitatesevaluation of the fusion cross section at each energy, and allows forthe calculation of a fusion rate in any incremental step. The fusionrate in the numerical case for each step is given by the equation (6):

$\begin{matrix}{{f_{n}(E)} = {n_{b}*\frac{I_{ion}}{e}*{\sigma\left( E_{n} \right)}*{\mathbb{d}l}}} & (6)\end{matrix}$

To calculate the total fusion rate, this equation was summed over allvalues of E_(n) until E=0 (or n*dl=the range of the particle) as shownin equation (7):

$\begin{matrix}{{F\left( E_{o} \right)} = {\sum\limits_{n = 0}^{{n*{dl}} = {range}}{f_{n}(E)}}} & (7)\end{matrix}$

This fusion rate is known as the “thick-target yield”. To solve this, aninitial energy was determined and a small step size dl chosen. Thefusion rate in the interval dl at full energy was calculated. Then theenergy for the next step was calculated, and the process repeated. Thisgoes on until the particle stops in the gas.

For the case of a singly ionized deuterium beam impacting a 10 torrhelium-3 gas background at room temperature, at an energy of 500 keV andan intensity of 100 mA, the fusion rate was calculated to beapproximately 2×10¹³ fusions/second, generating the same number of highenergy protons (equivalent to 3 μA protons). This level is sufficientfor the production of medical isotopes, as is known by those of skill inthe art. A plot showing the fusion rate for a 100 mA incident deuteriumbeam impacting a helium-3 target at 10 torr is shown in FIG. 21.

The fusion portions as described herein may be used in a variety ofdifferent applications. According to one construction, the fusionportions are used as a proton source to transmutate materials includingnuclear waste and fissile material. The fusion portions may also be usedto embed materials with protons to enhance physical properties. Forexample, the fusion portion may be used for the coloration of gemstones.The fusion portions also provide a neutron source that may be used forneutron radiography. As a neutron source, the fusion portions may beused to detect nuclear weapons. For example, as a neutron source thefusion portions may be used to detect special nuclear materials, whichare materials that can be used to create nuclear explosions, such as Pu,²³³U, and materials enriched with ²³³U or ²³⁵U. As a neutron source, thefusion portions may be used to detect underground features including butnot limited to tunnels, oil wells, and underground isotopic features bycreating neutron pulses and measuring the reflection and/or refractionof neutrons from materials. The fusion portions may be used as a neutronsource in neutron activation analysis (NAA), which may determine theelemental composition of materials. For example, NAA may be used todetect trace elements in the picogram range. As a neutron source, thefusion portions may also be used to detect materials including but notlimited to clandestine materials, explosives, drugs, and biologicalagents by determining the atomic composition of the material. The fusionportions may also be used as a driver for a sub-critical reactor.

The operation and use of the fusion portion 10, 11 is furtherexemplified by the following examples, which should not be construed byway of limiting the scope of the invention.

The fusion portions 10, 11 can be arranged in the magnetic configuration10 to function as a neutron source. In this arrangement, initially, thesystem 10 will be clean and empty, containing a vacuum of 10⁻⁹ torr orlower, and the high speed pumps 17 will be up to speed (two stages witheach stage being a turbomolecular pump). Approximately 25-30 standardcubic centimeters of gas (deuterium for producing neutrons) will beflowed into the target chamber 60 to create the target gas. Once thetarget gas has been established, that is, once the specified volume ofgas has been flowed into the system and the pressure in the targetchamber 60 reaches approximately 0.5 torr, a valve will be opened whichallows a flow of 0.5 to 1 sccm (standard cubic centimeters per minute)of deuterium from the target chamber 60 into the ion source 20. This gaswill re-circulate rapidly through the system, producing approximatelythe following pressures: in the ion source 20 the pressure will be a fewmtorr; in the accelerator 30 the pressure will be around 20 μtorr overthe pumping stage nearest the accelerator, the pressure will be <20μtorr; over the pumping stage nearest the target chamber, the pressurewill be approximately 50 mtorr; and in the target chamber 60 thepressure will be approximately 0.5 torr. After these conditions areestablished, the ion source 20 (using deuterium) will be excited byenabling the RF power supply (coupled to the RF antenna 24 by the RFmatching circuit) to about 10-30 MHz. The power level will be increasedfrom zero to about 500 W creating a dense deuterium plasma with adensity on the order of 10¹¹ particles/cm³. The ion extraction voltagewill be increased to provide the desired ion current (approximately 10mA) and focusing. The accelerator voltage will then be increased to 300kV, causing the ion beam to accelerate through the flow restrictions andinto the target chamber 60. The target chamber 60 will be filled with amagnetic field of approximately 5000 gauss (or 0.5 tesla), which causesthe ion beam to re-circulate. The ion beam will make approximately 10revolutions before dropping to a negligibly low energy.

While re-circulating, the ion beam will create nuclear reactions withthe target gas, producing 4×10¹⁰ and up to 9×10¹⁰ neutrons/sec for D.These neutrons will penetrate the target chamber 60, and be detectedwith appropriate nuclear instrumentation.

Neutral gas that leaks from the target chamber 60 into the differentialpumping section 40 will pass through the high speed pumps 17, through acold trap 13, 15, and back into the target chamber 60. The cold traps13, 15 will remove heavier gasses that in time can contaminate thesystem due to very small leaks.

The fusion portions 11 can also be arranged in the linear configurationto function as a neutron source. In this arrangement, initially, thesystem will be clean and empty, containing a vacuum of 10⁻⁹ torr orlower and the high speed pumps 17 will be up to speed (three stages,with the two nearest that accelerator being turbomolecular pumps and thethird being a different pump such as a roots blower). Approximately 1000standard cubic centimeters of deuterium gas will be flowed into thetarget chamber 70 to create the target gas. Once the target gas has beenestablished, a valve will be opened which allows a flow of 0.5 to 1 sccm(standard cubic centimeters per minute) from the target chamber 70 intothe ion source 20. This gas will re-circulate rapidly through thesystem, producing approximately the following pressures: in the ionsource 20 the pressure will be a few mtorr; in the accelerator 30 thepressure will be around 20 μtorr; over the pumping stage nearest theaccelerator, the pressure will be <20 μtorr; over the center pumpingstage the pressure will be approximately 50 mtorr; over the pumpingstage nearest the target chamber 70, the pressure will be approximately500 mtorr; and in the target chamber 70 the pressure will beapproximately 20 torr.

After these conditions are established, the ion source 20 (usingdeuterium) will be excited by enabling the RF power supply (coupled tothe RF antenna 24 by the RF matching circuit) to about 10-30 MHz. Thepower level will be increased from zero to about 500 W creating a densedeuterium plasma with a density on the order of 10¹¹ particles/cm³. Theion extraction voltage will be increased to provide the desired ioncurrent (approximately 10 mA) and focusing. The accelerator voltage willthen be increased to 300 kV, causing the ion beam to accelerate throughthe flow restrictions and into the target chamber 70. The target chamber70 will be a linear vacuum chamber in which the beam will travelapproximately 1 meter before dropping to a negligibly low energy.

While passing through the target gas, the beam will create nuclearreactions, producing 4×10¹⁰ and up to 9×10¹⁰ neutrons/sec. Theseneutrons will penetrate the target chamber 70, and be detected withappropriate nuclear instrumentation.

Neutral gas that leaks from the target chamber 70 into the differentialpumping section 40 will pass through the high speed pumps 17, through acold trap 13, 15, and back into the target chamber 70. The cold traps13, 15 will remove heavier gasses that in time can contaminate thesystem due to very small leaks.

In another construction, the fusion portions 10 are arranged in themagnetic configuration and are operable as proton sources. In thisconstruction, initially, the system will be clean and empty, containinga vacuum of 10⁻⁹ torr or lower, and the high speed pumps 17 will be upto speed (two stages with each stage being a turbomolecular pump).Approximately 25-30 standard cubic centimeters of gas (an approximate50/50 mixture of deuterium and helium-3 to generate protons) will beflowed into the target chamber 60 to create the target gas. Once thetarget gas has been established, that is, once the specified volume ofgas has been flowed into the system and the pressure in the targetchamber 60 reaches approximately 0.5 torr, a valve will be opened whichallows a flow of 0.5 to 1 sccm (standard cubic centimeters per minute)of deuterium from the target chamber 60 into the ion source 20. This gaswill re-circulate rapidly through the system, producing approximatelythe following pressures: in the ion source 20 the pressure will be a fewmtorr; in the accelerator 30 the pressure will be around 20 μtorr; overthe pumping stage nearest the accelerator 30, the pressure will be <20μtorr; over the pumping stage nearest the target chamber 60, thepressure will be approximately 50 mtorr; and in the target chamber 60the pressure will be approximately 0.5 torr. After these conditions areestablished, the ion source 20 (using deuterium) will be excited byenabling the RF power supply (coupled to the RF antenna 24 by the RFmatching circuit) to about 10-30 MHz. The power level will be increasedfrom zero to about 500 W creating a dense deuterium plasma with adensity on the order of 10¹¹ particles/cm³. The ion extraction voltagewill be increased to provide the desired ion current (approximately 10mA) and focusing. The accelerator voltage will then be increased to 300kV, causing the ion beam to accelerate through the flow restrictions andinto the target chamber 60. The target chamber 60 will be filled with amagnetic field of approximately 5000 gauss (or 0.5 tesla), which causesthe ion beam to re-circulate. The ion beam will make approximately 10revolutions before dropping to a negligibly low energy.

While re-circulating, the ion beam will create nuclear reactions withthe target gas, producing 1×10¹¹ and up to about 5×10¹¹ protons/sec.These protons will penetrate the tubes of the isotope extraction system,and be detected with appropriate nuclear instrumentation.

Neutral gas that leaks from the target chamber 60 into the differentialpumping section 40 will pass through the high speed pumps 17, through acold trap 13, 15, and back into the target chamber 60. The cold traps13, 15 will remove heavier gasses that in time can contaminate thesystem due to very small leaks.

In another construction, the fusion portions 11 are arranged in thelinear configuration and are operable as proton sources. In thisconstruction, initially, the system will be clean and empty, containinga vacuum of 10⁻⁹ torr or lower and the high speed pumps 17 will be up tospeed (three stages, with the two nearest that accelerator beingturbomolecular pumps and the third being a different pump such as aroots blower). Approximately 1000 standard cubic centimeters of about50/50 mixture of deuterium and helium-3 gas will be flowed into thetarget chamber 70 to create the target gas. Once the target gas has beenestablished, a valve will be opened which allows a flow of 0.5 to 1 sccm(standard cubic centimeters per minute) from the target chamber 70 intothe ion source 20. This gas will re-circulate rapidly through thesystem, producing approximately the following pressures: in the ionsource 20 the pressure will be a few mtorr; in the accelerator 30 thepressure will be around 20 μtorr; over the pumping stage nearest theaccelerator 30, the pressure will be <20 μtorr over the center pumpingstage the pressure will be approximately 50 mtorr; over the pumpingstage nearest the target chamber 70, the pressure will be approximately500 mtorr; and in the target chamber 70 the pressure will beapproximately 20 torr.

After these conditions are established, the ion source 20 (usingdeuterium) will be excited by enabling the RF power supply (coupled tothe RF antenna 24 by the RF matching circuit) to about 10-30 MHz. Thepower level will be increased from zero to about 500 W creating a densedeuterium plasma with a density on the order of 10¹¹ particles/cm³. Theion extraction voltage will be increased to provide the desired ioncurrent (approximately 10 mA) and focusing. The accelerator voltage willthen be increased to 300 kV, causing the ion beam to accelerate throughthe flow restrictions and into the target chamber 70. The target chamber70 will be a linear vacuum chamber in which the beam will travelapproximately 1 meter before dropping to a negligibly low energy.

While passing through the target gas, the beam will create nuclearreactions, producing 1×10¹¹ and up to about 5×10¹¹ protons / sec. Theseprotons will penetrate the walls of the tubes of the isotope extractionsystem, and be detected with appropriate nuclear instrumentation.

Neutral gas that leaks from the target chamber 70 into the differentialpumping section 40 will pass through the high speed pumps 17, through acold trap 13, 15, and back into the target chamber 70. The cold traps13, 15 will remove heavier gasses that in time can contaminate thesystem due to very small leaks.

In another construction, the fusion portions 10, 11 are arranged ineither the magnetic configuration or the linear configuration and areoperated as neutron sources for isotope production. The system will beoperated as discussed above with the magnetic target chamber or with thelinear target chamber 70. A solid sample, such as solid foil of parentmaterial ⁹⁸Mo will be placed proximal to the target chamber 60, 70.Neutrons created in the target chamber 60, 70 will penetrate the wallsof the target chamber 60, 70 and react with the ⁹⁸Mo parent material tocreate ⁹⁹Mo, which may decay to meta-stable ⁹⁹Tn. The ⁹⁹Mo will bedetected using suitable instrumentation and technology known in the art.

In still other constructions, the fusion portions 10, 11 are arranged asproton sources for the production of isotopes. In these construction,the fusion portion 10, 11 will be operated as described above with themagnetic target chamber 60 or with the linear target chamber 70. Thesystem will include an isotope extraction system inside the targetchamber 60, 70. Parent material such as water comprising H₂ ¹⁶O will beflowed through the isotope extraction system. The protons generated inthe target chamber will penetrate the walls of the isotope extractionsystem to react with the ¹⁶O to produce ¹³N. The ¹³N product materialwill be extracted from the parent and other material using an ionexchange resin. The ¹³N will be detected using suitable instrumentationand technology known in the art.

In summary, each fusion portion 10, 11 provides, among other things, acompact high energy proton or neutron source. The foregoing descriptionis considered as illustrative only of the principles of the fusionportion 10, 11. Further, since numerous modifications and changes willreadily occur to those skilled in the art, it is not desired to limitthe fusion portion 10, 11 to the exact construction and operation shownand described, and accordingly, all suitable modifications andequivalents may be resorted to as required or desired.

As illustrated in FIGS. 22 and 23, the fission portions 400 a, 400 b ofthe hybrid reactor 5 a, 5 b are positioned adjacent the target chambers60, 70 of a plurality of fusion portions 10, 11. The fusion portions 10,11 are arranged such that a reaction space 405 is defined within thetarget chambers 60, 70. Specifically, the ion trajectories within thetarget chambers 60, 70 do not enter the reaction space 405, and somaterials to be irradiated can be placed within that volume. In order tofurther increase the neutron flux, multiple fusion portions 10, 11 arestacked on top of one another, with as many as ten sources beingbeneficial. As illustrated in FIG. 22, the hybrid reactor 5 a includesthe fission portion 400 a and fusion portions 10 in the magneticarrangement to produce a plurality of stacked target chambers 60 thatare pancake shaped but in which the ion beam flows along an annularpath. Thus, the reaction space 405 within the annular path can be usedfor the placement of materials to be irradiated.

FIG. 23 illustrates a linear arrangement of the fusion portions 11coupled to the fission portion 400 b to define the hybrid reactor 5 b.In this construction, the ion beams are directed along a plurality ofsubstantially parallel, spaced-apart linear paths positioned within anannular target chamber 70. The reaction space 405 within the annulartarget chamber 70 is suitable for the placement of materials to beirradiated. Thus, as will become apparent, the fission portions 400 a,400 b described with regard to FIGS. 24-29 could be employed with eitherthe magnetic configuration or the linear configuration of the fusionportions 10, 11.

With reference to FIGS. 22 and 23 the fission portion 400 a, 400 bincludes a substantially cylindrical activation column 410 (sometimesreferred to as an activation cell) positioned within a tank 415 thatcontains a moderator/reflector material selected to reduce the radiationthat escapes from the fission portion 400 a, 400 b during operation. Theactivation column 410 is positioned within the target chamber 60, 70where the fusion reactions occur. The target chamber 60, 70 is about 1 mtall. A layer of beryllium 420 may surround the target chamber 60, 70.The moderating material is typically D₂O or H₂O. In addition, a gasregeneration system 425 is positioned on top of the tank 415. Anaperture 430 in the center of the gas regeneration system 425 extendsinto the activation column 410 where a sub-critical assembly 435including a LEU mixture and/or other parent material may be located. Inpreferred constructions, the aperture 430 has about a 10 cm radius andis about 1 m long.

Each fusion portion 10, 11 is arranged to emit high energy neutrons fromthe target chamber. The neutrons emitted by the fusion portions 10, 11are emitted isotropically, and while at high energy those that enter theactivation column 410 pass through it with little interaction. Thetarget chamber is surrounded by 10-15 cm of beryllium 420, whichmultiplies the fast neutron flux by approximately a factor of two. Theneutrons then pass into the moderator where they slow to thermal energyand reflect back into the activation cell 410.

It is estimated that the neutron production rate from this configurationis about 10¹⁵ n/s (the estimated source strength for a single fusionportion 10, 11 operating at 500 kV and 100 mA is 10¹⁴ n/s and there areten of these devices in the illustrated construction). The totalvolumetric flux in the activation cell 410 was calculated to be2.35*10¹² n/cm²/s with an uncertainty of 0.0094 and the thermal flux(less than 0.1 eV) was 1.34*10¹² n/cm²/s with an uncertainty of 0.0122.This neutron rate improves substantially with the presence of LEU aswill be discussed.

As discussed with regard to FIGS. 1 and 3, the fusion portion 10, 11 canbe arranged in the magnetic arrangement or the linear arrangement. Thereal advantage of the magnetic arrangement of the fusion portions 10, 11is that they allow for a long path length in a relatively low pressuregas. To effectively use the linear configuration, the target gas must becooled and must be maintained at a higher pressure. One example of sucha configuration would have several deuterium beam lines shooting axiallyinto the target chamber 70 from above and below the device asillustrated in FIG. 23. While the target chambers 70 may need to operateat up to 10 torr for this to be successful, it may be a simpler and moreefficient approach for the fusion portion 10, 11.

The primary simplification in the linear configuration is theelimination of the components needed to establish the magnetic fieldthat guides the beam in the spiral or helical pattern. The lack of thecomponents needed to create the field makes the device cheaper and themagnets do not play a role in attenuating the neutron flux. However, insome constructions, a magnetic field is employed to collimate the ionbeam produced by the linear arrangement of the fusion portions 11, aswill be discussed.

In order to produce ⁹⁹Mo of high specific activity as an end product, itshould be made from a material that is chemically different so that itcan be easily separated. The most common way to do this is by fission of²³⁵U through neutron bombardment. The fusion portions 10, 11 describedpreviously create sufficient neutrons to produce a large amount of ⁹⁹Mowith no additional reactivity, but if ²³⁵U is already present in thedevice, it makes sense to put it in a configuration that will provideneutron multiplication as well as providing a target for ⁹⁹Moproduction. The neutrons made from fission can play an important role inincreasing the specific activity of the ⁹⁹Mo, and can increase the total⁹⁹Mo output of the system. The multiplication factor, k_(eff) is relatedto the multiplication by equation 1/(1−k_(eff)). This multiplicationeffect can result in an increase of the total yield and specificactivity of the end product by as much as a factor of 5-10. k_(eff) is astrong function of LEU density and moderator configuration.

Several subcritical configurations of subcritical assemblies 435 whichconsist of LEU (20% enriched) targets combined with H₂O (or D₂O) arepossible. All of these configurations are inserted into the previouslydescribed reaction chamber space 405. Some of the configurationsconsidered include LEU foils, an aqueous solution of a uranium saltdissolved in water, encapsulated UO₂ powder and others. The aqueoussolutions are highly desirable due to excellent moderation of theneutrons, but provide challenges from a criticality perspective. Inorder to ensure subcritical operation, the criticality constant, k_(eff)should be kept below 0.95. Further control features could easily beadded to decrease k_(eff) if a critical condition were obtained. Thesecontrol features include, but are not limited to control rods,injectable poisons, or pressure relief valves that would dump themoderator and drop the criticality.

Aqueous solutions of uranium offer tremendous benefits for downstreamchemical processes. Furthermore, they are easy to cool, and provide anexcellent combination of fuel and moderator. Initial studies wereperformed using a uranium nitrate solution-UO₂(NO₃)₂, but othersolutions could be considered such as uranium sulfate or others. In oneconstruction, the salt concentration in the solution is about 66 g ofsalt per 100 g H₂O. The solution is positioned within the activationcell 410 as illustrated in FIGS. 24 and 25. In addition to the solution,there is a smaller diameter cylinder 500 in the center of the activationcell 410 filled with pure water. This cylinder of water allows the valueof k_(eff) to be reduced so that the device remains subcritical, whilestill allowing for a large volume of LEU solution to be used.

In the aqueous solution layout illustrated in FIGS. 24 and 25, thecentral most cylinder 500 contains pure water and is surrounded by anaqueous mixture of uranium nitrate that is contained between the tubeand a cylindrical wall 505 that cooperate to define a substantiallyannular space 510. The target chamber 60, 70 is the next most outwardlayer and is also annular. The pure water, the aqueous mixture ofuranium nitrate, and the target chamber 60, 70 are surrounded by the Bemultiplier/reflector 420. The outermost layer 520 in this case is alarge volume of D₂O contained within the tank 415. The D₂O acts as amoderator to reduce radiation leakage from the fission portion 400 a,400 b. FIGS. 26-29 illustrate similar structural components but containdifferent materials within some or all of the volumes as will bediscussed with those particular figures.

A common method to irradiate uranium is to form it into either uraniumdioxide pellets or encase a uranium dioxide powder in a container. Theseare inserted into a reactor and irradiated before removal andprocessing. While the UO₂ powders being used today utilize HEU, it ispreferable to use LEU. In preferred constructions, a mixture of LEU andH₂O that provides K_(eff)<0.95 is employed.

FIGS. 26 and 27 illustrate an activation column 410 that includes UO₂ ina homogeneous solution with D₂O. The center cylinder 500 in thisconstruction is filled with H₂O 525, as is the outermost layer 530 (onlya portion of which is illustrated). The first annular space 535 containsa solution of 18% LEU (20% enriched) and 82% D₂O. The second annularlayer 540 is substantially evacuated, consistent with the fusion portiontarget chambers 60, 70. The center cylinder 500, the first annular space535, and the second annular space 540 are surrounded by a layer of Be420, which serves as a multiplier and neutron reflector.

In another construction, ⁹⁹Mo is extracted from uranium by chemicaldissolution of LEU foils in a modified Cintichem process. In thisprocess, thin foils containing uranium are placed in a high flux regionof a nuclear reactor, irradiated for some time and then removed. Thefoils are dissolved in various solutions and processed through multiplechemical techniques.

From a safety, non-proliferation, and health perspective, a desirableway to produce ⁹⁹Mo is by (n,γ) reactions with parent material ⁹⁸Mo.This results in ⁹⁹Mo with no contamination from plutonium or otherfission products. Production by this method also does not require aconstant feed of any form of uranium. The disadvantage lies in thedifficulty of separating ⁹⁹Mo from the parent ⁹⁸Mo, which leads to lowspecific activities of ⁹⁹Mo in the generator. Furthermore, the cost ofenriched ⁹⁸Mo is substantial if that is to be used. Still, considerableprogress has been made in developing new elution techniques to extracthigh purity ^(99m)Tc from low specific activity ⁹⁹Mo, and this maybecome a cost-effective option in the near future. To implement thistype of production in the hybrid reactor 5 a, 5 b illustrated herein, afixed subcritical assembly 435 of LEU can be used to increase theneutron flux (most likely UO₂), but can be isolated from the parent⁹⁸Mo. The subcritical assembly 435 is still located inside of the fusionportion 10, 11, and the ⁹⁹Mo activation column would be located withinthe subcritical assembly 435.

In preferred constructions, ⁹⁸Mo occupies a total of 20% of theactivation column 410 (by volume). As illustrated in FIGS. 28 and 29,the centermost cylinder 500 contains a homogeneous mixture of 20% ⁹⁸Moand H₂O. The first annular layer 555 includes a subcritical assembly 435and is comprised of an 18% LEU (20% enriched)/D₂O mixture. The secondannular layer 560 is substantially evacuated, consistent with the fusionportion target chambers 60, 70. The center cylinder 500, the firstannular space 555, and the second annular space 560 are surrounded bythe layer of Be 420, which serves as a multiplier and neutron reflector.The outermost layer 570 (only a portion of which is illustrated)contains water that reduces the amount of radiation that escapes fromthe fission portion 5 a, 5 b.

For the LEU cases, the production rate and specific activity of ⁹⁹Mo wasdetermined by calculating 6% of the fission yield, with a fusion portion10, 11 operating at 10¹⁵ n/s. K_(eff) was calculated for variousconfigurations as well. Table 1 summarizes the results of thesecalculations. In the case of production from ⁹⁸Mo, an (n,γ) tally wasused to determine the production rate of ⁹⁹Mo. The following tableillustrates the production rates for various target configurations inthe hybrid reactor 5 a, 5 b.

⁹⁹Mo yield/g Total ⁹⁹Mo yield U (or ⁹⁸Mo) @ saturation TargetConfiguration K_(eff) (Ci) (6 day kCi) Aqueous UO₂(NO₃)₂ 0.947 1.51 2.93UO₂ powder 0.945 2.92 22 Natural Mo (w subcritical) 0.943 0.68 2.69 ⁹⁸Mo(w subcritical) 0.943 2.83 11.1 Natural Mo (w/o subcritical) — 0.0850.44 ⁹⁸Mo (w/o subcritical) — 0.35 1.8

While the specific activity of ⁹⁹Mo generated is relatively constant forall of the subcritical cases, some configurations allow for asubstantially higher total production rate. This is because theseconfigurations allow for considerably larger quantities of parentmaterial. It is also worth noting that production of ⁹⁹Mo from ⁹⁸Mo isas good a method as production from LEU when it comes to the totalquantity of ⁹⁹Mo produced. Still, the LEU process tends to be morefavorable as it is easier to separate ⁹⁹Mo from fission products than itis to separate it from ⁹⁸Mo, which allows for a high specific activityof ⁹⁹Mo to be available after separation.

In constructions in which ⁹⁸Mo is used to produce ⁹⁹Mo, the subcriticalassembly 435 can be removed altogether. However, if the subcriticalassembly 435 is removed, the specific activity of the end product willbe quite a bit lower. Still, there are some indications that advancedgenerators might be able to make use of the low specific activityresulting from ⁹⁸Mo irradiation. The specific activity produced by thehybrid reactor 5 a, 5 b without subcritical multiplication is highenough for some of these technologies. Furthermore, the total demand forU.S. ⁹⁹Mo could still be met with several production facilities, whichwould allow for a fission free process.

For example, in one construction of a fusion only reactor, thesubcritical assembly 435 is omitted and ⁹⁸Mo is positioned within theactivation column 410. To enhance the production of ⁹⁹Mo, a morepowerful ion beam produced by the linear arrangement of the fusionportion 11 is employed. It is preferred to operate the ion beams at apower level approximately ten times that required in the aforementionedconstructions. To achieve this, a magnetic field is established tocollimate the beam and inhibit the undesirable dispersion of the beams.The field is arranged such that it is parallel to the beams andsubstantially surrounds the accelerator 30 and the pumping system 40 butdoes not necessarily extend into the target chamber 70. Using thisarrangement provides the desired neutron flux without the multiplicativeeffect produced by the subcritical assembly 435. One advantage of thisarrangement is that no uranium is required to produce the desiredisotopes.

Thus, the invention provides, among other things, a new and usefulhybrid reactor 5 a, 5 b for use in producing medical isotopes. Theconstructions of the hybrid reactor 5 a, 5 b described above andillustrated in the figures are presented by way of example only and arenot intended as a limitation upon the concepts and principles of theinvention. Various features and advantages of the invention are setforth in the following claims.

What is claimed is:
 1. A hybrid reactor operable to produce a medicalisotope, the reactor comprising: an ion source operable to produce anion beam from a gas; a target chamber including a target that interactswith the ion beam to produce neutrons via a fusion reaction, wherein thetarget comprises deuterium, tritium, or helium, or a combinationthereof; and an annular activation cell positioned proximate the targetchamber and including a parent material that interacts with the neutronsto produce the medical isotope via a fission reaction, wherein theparent material is in an aqueous solution, wherein the water of theaqueous solution acts as a moderator, and wherein the fission reactionis maintained at a subcritical level with neutron multiplication.
 2. Thehybrid reactor of claim 1, wherein RF resonance is used to produce theion beam.
 3. The hybrid reactor of claim 1, further comprising anaccelerator positioned between the ion source and the target chamber andoperable to accelerate the ions of the ion beam.
 4. The hybrid reactorof claim 1, wherein the gas includes one of deuterium and tritium andthe target includes the other of deuterium and tritium.
 5. The hybridreactor of claim 1, wherein the target chamber defines a long targetpath that is substantially linear.
 6. The hybrid reactor of claim 5,further comprising at least one magnet positioned to define a magneticfield that collimates the ion beam within at least a portion of the longtarget path.
 7. The hybrid reactor of claim 1, wherein the targetchamber defines a long target path that is substantially helical.
 8. Thehybrid reactor of claim 7, further comprising at least one magnetpositioned to define a magnetic field that directs the ion beam alongthe helical path.
 9. The hybrid reactor of claim 1, wherein the ionsource and the target chamber together at least partially define one ofa plurality of fusion reactors.
 10. The hybrid reactor of claim 9,wherein the target chamber of each of the plurality of fusion reactorscooperate to substantially surround a cylindrical space.
 11. The hybridreactor of claim 10, wherein the activation cell is substantiallyannular and is positioned within the cylindrical space.
 12. The hybridreactor of claim 1, further comprising a reflector positioned proximatethe target chamber and selected to reflect neutrons toward theactivation cell.
 13. The hybrid reactor of claim 1, wherein the parentmaterial comprises uranium enriched to 20% or less of ²³⁵U and themedical isotope is ⁹⁹Mo.
 14. The hybrid reactor of claim 1, furthercomprising an attenuator positioned proximate the activation cell andselected to maintain the fission reaction at a subcritical level. 15.The hybrid reactor of claim 12, wherein the attenuator is positionedinside of the annular activation cell and the reflector substantiallysurrounds the plurality of target chambers.
 16. A hybrid reactoroperable to produce a medical isotope, the reactor comprising: an ionsource operable to produce an ion beam from a gas; a target chamberincluding a target that interacts with the ion beam to produce neutronsvia a fusion reaction, wherein the target comprises deuterium, tritium,or helium, or a combination thereof; and an annular activation cellpositioned proximate the target chamber and including an aqueoussolution comprising a parent material that interacts with the neutronsto produce the medical isotope via a fission reaction, wherein the waterof the aqueous solution acts as a moderator, and wherein the fissionreaction is maintained at a subcritical level with neutronmultiplication.
 17. The hybrid reactor of claim 1, further comprising anadditional moderator substantially surrounding the activation cell.